1. Field of the Invention
The present invention relates to a call restriction system for an ATM exchange.
An ATM (asynchronous transmission mode) exchange system which provides services using ATM as recommended by the ITU-T (formerly the CCITT) has been proposed as implementation of a broadband ISDN (integrated service digital network) which is seen as the infrastructure for the next-generation of data communication systems.
2. Description of Related Art
In an ATM exchange, data to be communicated, at speeds ranging from several tens of bps to several hundred Mbps, is all divided in to packets (cells) of a fixed length of 0 to approximately 128 octets, these being then mixed on a transmission path of 150 Mbps or greater, with high-speed processing being performed by high-speed packet switching.
In previous non-ATM exchanges, call restriction processing was either performed by means of software in the exchange control processor or was performed overall for all circuits which are under the control of the firmware which controls a circuit interface section.
Call restriction is performed as a means of preventing an increase in load when the exchange becomes overloaded, and in a system in which call restriction is performed by the control processor of an exchange, the call restriction itself causes an increase in the load on the exchange's control processor, thereby itself leading to a increase in the load on the exchange.
In an exchange which has firmware in a circuit interface section which controls the circuit interface, it is this firmware which performs call restriction. A switching system comprises a circuit interface section, a call control processor, and call-processing software, with a plurality of physical circuits connected to the above-noted circuit interface section. These physical circuits are connected either to subscribers or to other relay equipment.
Within the above-noted circuit interface section is provided control firmware for the purpose of performing call restriction processing, and when data for the purpose of call restriction is received by the call-processing software, a call restriction program is started up, in accordance with the call-processing software. In the case in which it has become necessary to perform call restriction, a call restriction request is made to the circuit interface section, in response to the receipt of which the circuit interface section control firmware performs call restriction with respect to all the physical circuits that are connected to its own circuit interface section.
In this system, because part of the load of the call control processor is shifted to the control firmware, there is a reduction in the processing load on the call control processor. However, when performing restriction processing by control firmware, because restriction is performed for all physical circuits connected to the local circuit interface, there is the problem of excessive restriction.
In an ATM exchange, so-called call restriction or incoming/outgoing restriction in the past was not performed, there being only originating call restriction by means of, for example, a command issued by a maintenance personnel in the station-to-station interface. The physical circuits in an ATM exchange are large-capacity circuits which terminate ATM cells, which exist as virtual paths (VPs) and virtual channels (VCs), and at present rather than subscriber terminals being directly connected to these physical circuits, frame relays and packet exchanges are connected, with a plurality of subscriber terminals which are mapped onto the above-noted physical channels being connected via an LAN gateway or the like. If call restriction or incoming/outgoing restriction is to be performed in an ATM exchange as well, and if restriction is performed for each individual circuit (logical circuit) as in the past, while it is possible to expect a reduction in call loss, this would result in a significant increase in the associated processing load.